There are several variables affecting the success of restoration in posterior root filled teeth. These include quality of the work, type of restoration and host-related factors. Recommending the best approach in any given patient is an important clinical decision that required balancing a range of demands.

The aim of this review was to identify the literature published on the failure rate of conventional single-unit restorations in root filled posterior permanent teeth.

Methods

Searches were conducted in the Medline, Embase, Cochrane CENTRAL and Cochrane Oral Health Group Trials Register supplemented by hand searches of the journals;Journal of Prosthodontics, International Journal of Prosthodontics, Journal of Prosthetic Dentistry, The International Journal of Periodontics and Restorative Dentistry, Journal of Dental Research, Journal of Operative Dentistry, Journal of the American Dental Association, Journal of Dentistry, The International Endodontic Journal and The Journal of Endodontics between 2005-14. Randomised controlled trials (RCTs) and observational studies reporting on clinical or radiographic failure of restorations on root filled teeth with or without a post and core were considered

Two reviewers independently selected studies abstracted data and assessed study quality. RCTs were assessed using the Cochrane risk of bias tool, observation studies using the STROBE (Strengthening the Reporting of Observational studies in Epidemiology) statement and Olmos classification. Overall quality was assessed using the American Association of Critical-Care Nurses evidence-levelling system. Pooled mean failure rates were reported according to the type of treatment and remaining coronal tooth structure. As meta-analysis was not possible a narrative summary was presented.

Results

5 studies (4 RCTs,1 Observational studies) involving a total of 955 patients and 1160 direct and indirect restorations were included.

Post-retained crowns were associated with the most favourable outcome in teeth with one to two remaining coronal tooth wall(s), whereas post-free crowns were superior when greater tooth structure was available

Conclusions

The authors concluded

Most of the information obtained was retrieved from studies with high risk of bias; therefore, the results should be interpreted with caution. However, despite limitations, the study provided two main conclusions regarding restorations on posterior root filled teeth:

The greater the amount of remaining tooth structure, the better the treatment outcome.

Post-retained crowns seem to be the superior treatment, followed by post-free crowns and intracoronal restorations.

Accordingly, endodontic access cavities should be kept conservative to maximize the amount of remaining tooth structure, which in turn should determine the choice of dental restoration. Despite the superiority of post-retained crowns, post-free crowns can be considered when there are three to four walls left, whereas post-retained crowns may be preferred in teeth with one to two walls left. Other prosthetic replacements may be considered in cases with <1 wall left, especially with no ferrule.

Comments

Despite a good database and journal search the authors only identified a small number of papers to assess this relatively common clinical question. Two earlier reviews (Dental Elf – 3rd Aug 2015; Dental Elf – 5th Jul 2011) have tackled this the other way around looking at root canal treatment failures rather than restoration failures, the main thrust of this review. While the authors have drawn some clear conclusions the underlying evidence is quite limited and high quality evidence is required. This would be aided by agreement on the use of common outcome reporting to assist comparisons.

Derek Richards is the Director of the Centre for Evidence-based Dentistry, Editor of the Evidence-based Dentistry Journal, Consultant in Dental Public Health with Forth Valley Health Board and Honorary Senior Lecturer at Dundee & Glasgow Dental Schools. He helped to establish both the Centre for Evidence-based Dentistry and the Evidence-based Dentistry Journal. He has been involved with teaching EBD and a wide range of evidence-based initiatives both nationally and internationally since 1994.